In recent years, an image reading apparatus such as a scanner is used in which two optical units having an image capturing device or an illumination unit are provided to face each other across a document conveyance path. In the image reading apparatus when images of documents having various thicknesses are captured such as a copy paper, a thick paper, a plastic card etc., to prevent the occurrence of an out-of-focus, an unevenness of brightness etc., one optical unit is movably provided depending on the thickness of the document to be conveyed.
A copying machine including a CIS having its reading surface coated to prevent reading vertical stripes generated as a paste-like foreign object attached to a document adheres to the reading surface is disclosed. The copying machine detects the thickness of the document and adjusts the gap between the glass surface of the CIS and the roller portion of a reading roller in accordance with the detection result (see patent literature 1).